Generally, a semiconductor device is fabricated by sealing a semiconductor IC chip in a prescribed package and mounting the package on a package substrate. There are various kinds of packages according to the respective uses and kinds of IC chips included therein.
FIG. 9(a) is a perspective view illustrating a general-purpose plastic molded package a an example of the above-described semiconductor IC packages. In FIG. 9(a), reference numeral 700 designates the plastic molded package. A semiconductor IC chip 3 is disposed on a die pad of a lead frame, and electrode pads of the IC chip 3 are connected to lead terminals of the lead frame by bonding wires or the like. Then, the IC chip 3 on the lead frame is encapsulated in a molded plastic 701, and external lead terminals 702 are downwardly bent with respect to the plane surface of the lead frame on which the chip 3 is disposed. The external lead terminals 702 thus bent serve as lead pins for connecting the package 700 to a package substrate.
A method of mounting the plastic molded package 700 on the package substrate will be described. Initially, a printed circuit board (not shown) is prepared. A conductive layer having a prescribed wiring pattern is printed on the rear surface of the board and holes for the lead pins 702 of the package 700 are formed through the board. Then, end portions 702a of the lead pins 702 are inserted in the through-holes from the surface side of the printed circuit board and connected to the conductive layer on the rear surface of the board by solder or the like.
In the above-described method for mounting the conventional package 700, however, since the lead pins 702 of the package are connected to the conductive layer on the rear surface of the printed circuit board, the package is mounted on only one side of the printed circuit board so that high-density mounting is not achieved.
In order to solve this problem, surface mountable packages have been used in recent years. FIG. 9(b) is a perspective view illustrating the conventional surface mountable package disclosed in Japanese Published Patent Application No. 4-25036. In FIG. 9(b), reference numeral 600 designates the surface mountable package. Lead pins 602 are bent so that end portions 602a are level with the rear surface of the plastic package 601. When the package is mounted on a package substrate, the end portions 602a are put on a conductive layer on the surface of the package substrate and adhered to the conductive layer by solder or the like, whereby the lead pins and the wiring on the package substrate are connected to each other on the surface of the package substrate whereon the package is mounted. That is, packages can be mounted on both surfaces of the package substrate.
In addition, the surface mountable package 600 can be filled with a high frequency semiconductor IC chip (hereinafter referred to as microwave IC chip) using the lead pins 602 appropriately as grounding pins or signal pins. In this case, however, since the lead pins 602 are merely wires, the line inductance of each lead pin significantly increases in a high frequency band, thereby deteriorating performance of the microwave IC chip. In order to solve the problem in the high frequency band, there is a microwave IC package in which a coplanar line including a grounding lead pin and a signal lead pin which are connected to a grounding terminal and a signal terminal of the IC chip by bonding wires, respectively. The above-described Japanese Published Patent Application No. 4-25036 also discloses a microwave IC package of this kind.
In the above-described surface mountable package, however, the molded plastic having a certain dielectric constant is closely adhered to the microwave IC chip, so that characteristics of the IC chip in the design stage are unfavorably changed or deteriorated due to the molded plastic. In addition, the lead frame and the IC chip are encapsulated together in the molded plastic after the die bonding and the wire bonding are performed, so that the packaging is complicated. Therefore, it is difficult to provide a plurality of IC packages including different function IC chips in a short time in compliance with the requests of the user.
In order to solve the above-described problems, an improved surface mountable package has been developed, which can complete the packaging by only disposing a microwave IC chip on a package body and putting a lid thereon. This package avoids deterioration in the characteristics of the microwave IC chip and promptly meets the user's demand.
FIGS. 10, 11(a)-11(c), and 12(a)-12(b) are diagrams for explaining the improved surface mountable microwave IC package. More specifically, FIG. 10 is a perspective view, partly broken away, illustrating the external appearance and the internal structure of the package. FIG. 11(a) is a bottom view of the package, FIG. 11(b) is a side elevational view thereof, and FIG. 11(c) is a cross-sectional view taken along a line XIc--XIc of FIG. 11(a). FIGS. 12(a) and 12(b) are a perspective view and a front elevational view, respectively, for explaining a method of mounting the package on a package substrate.
In these figures, a surface mountable package 500 comprises a package body 501 on which a microwave IC chip 1 is disposed and a lid 590 put on the package body 501.
The package body 501 comprises a ceramic substrate 501a and a ground conductor layer 501b. Portions of the ground conductor layer 501b are selectively removed to form U-shaped gaps 502a and 502b, whereby an input side coplanar transmission line part 550 and an output side coplanar transmission line part 560 are formed, respectively.
More specifically, a portion 552 of the conductor layer 501b surrounded by the U-shaped gap 502a serves as a coplanar signal conductor of the input side coplanar transmission line part 550, and portions 551 and 553 of the conductor layer 501b serve as ground conductors. Similarly, a portion 562 of the conductor layer 501b surrounded by the U-shaped gap 502b serves as a coplanar signal conductor of the output side coplanar transmission line part 560, and portions 561 and 563 of the conductor layer 501b serve as ground conductors. As shown in FIG. 11(b), a width W of the coplanar signal conductor 552 (562) and intervals G between the signal conductor 552 (562) and the ground conductors 551 and 553 (561 and 563) are chosen so that characteristic impedance of the coplanar transmission line part 550 (560) is 50.OMEGA..
The input side signal conductor 552 and the output side signal conductor 562 are connected to an input side signal lead 512 and an output side signal lead 522, respectively. The input side ground conductors 551 and 553 and the output side ground conductors 561 and 563 are connected to input side ground leads 511 and 513 and output side ground leads 521 and 523. An input terminal 510 comprises the leads 511 to 513 and an output terminal 520 comprises the leads 521 to 523. When the package is mounted on a package substrate 601, the input and output terminals 510 and 520 are connected to coplanar transmission lines 610 and 620 on the package substrate, respectively.
Meanwhile, on the surface of the ceramic substrate 501a, conductor layers 503a and 503b are disposed at positions opposite to the coplanar signal conductors 552 and 562, respectively. The conductor layer 503a serves as a strip signal conductor of the input side microstrip transmission line part 570, and portions of the ceramic substrate 501a opposite to the portions 551 and 553 of the ground conductor layer 501b serve as ground conductors of the input side microstrip transmission line part 570. Similarly, the conductor layer 503b serves as a strip signal conductor of the output side microstrip transmission line part 580, and portions of the ceramic substrate 501a opposite to the portions 561 and 563 of the ground conductor layer 501b serve as ground conductors of the output side microstrip transmission line part 580. The width of the strip signal conductor 503a (503b) and the thickness and a dielectric constant of the ceramic substrate 501a are appropriately chosen so that the characteristic impedance of the microstrip transmission line part 570 (580) is 50.OMEGA.. In addition, the strip signal conductors 503a and 503b on the surface of the ceramic substrate 501a are connected to the coplanar transmission lines 552 and 562 on the rear surface of the ceramic substrate via through-holes 504a and 504b filled with a conductive material, respectively.
Through-holes 505 filled with a conductive material are located in a region of the ceramic substrate 501a where the microwave IC chip 1 is disposed. When the IC chip 1 is disposed on the region of the ceramic substrate 501a, a ground conductor film 1a of the IC chip 1 is connected to the ground conductor layer 501b on the rear surface of the package via the through-holes 505.
A description is given of a method for mounting the microwave IC package on the package substrate.
Initially, the microwave IC chip 1 is adhered to the package body 501 with a conductive adhesive or the like, and input and output side electrode pads (not shown) on the surface of the chip 1 are connected to the input and output side strip signal conductors 503a and 503b by bonding wires 2a and 2b, respectively. Then, the lid 590 is put on the package body 501 and adhered to the package body with an adhesive or the like. The lid 590 provides both a hermetic seal and shielding.
Then, as illustrated in FIG. 12(a), the microwave IC package 500 is mounted on the package substrate 601. On the package substrate 601, are disposed a coplanar transmission line 610 for applying microwave signals to the microwave IC chip 1 and a coplanar transmission line 620 for transferring microwave signals from the IC chip 1 to the subsequent stage. The coplanar transmission lines 610 and 620 are connected to the input terminal 510 and the output terminal 520 of the package 500, respectively.
More specifically, when the microwave IC package 500 is put at a prescribed position of the package substrate 601, the signal lead 512 of the input terminal 510 contacts the signal conductor 612 of the coplanar transmission line 610 while the signal lead 522 of the terminal 520 contacts signal conductor 622 of the coplanar transmission line part 620. The ground leads 511 and 513 of the input terminal 510 contact the ground conductors 611 and 613 of the coplanar transmission line 610 while the ground leads 521 and 523 of the output terminal 520 contact the ground conductors 621 and 623 of the coplanar transmission line 620. Then, the respective contacting parts are fixed by solder or the like, whereby the microwave IC package 500 is mounted on the package substrate 601.
Then, another microwave IC package 500 is mounted on the rear surface of the package substrate 601 in the same manner as described above (FIG. 12(b)). In this way, microwave IC packages 500 are mounted on both surfaces of the package substrate 601, resulting in a high-density mounting hybrid IC.
Japanese Published Patent Application No. 2-106707 discloses a hybrid IC in which an end of a microstrip line on a package substrate is used as a terminal for an I/O interface with an external circuit.
In the microwave IC package 500 thus mounted on the package substrate 601, a microwave input applied to the input terminal 510 from the signal supply side coplanar line 610 travels through the input side coplanar transmission line part 550 on the rear surface of the package body and the through-hole 504a and reaches the input side microstrip transmission line part 570 on the surface of the package body. Then, the microwave signal travels through the bonding wire 2a to reach the microwave IC chip 1.
Thereafter, the microwave signal is subjected to a prescribed signal processing, for example, amplification, switching, phase modification, or the like according to the function of the IC chip, and then it is output from the IC chip 1. The microwave signal output travels through the bonding wire 2b, the output side microstrip transmission line part 580, and the through-hole 504b to reach the output side coplanar transmission line part 560. Then, it is output to the signal transfer side coplanar line 620 on the package substrate 601 from the output terminal 520 of the package 500.
In the prior art surface mountable microwave IC package 500, the strip signal conductors 503a and 503b disposed on the surface of the ceramic substrate 501a are connected to the coplanar signal conductors 552 and 562 on the rear surface of the ceramic substrate 501a by the through-holes 504a and 504b which are filled with conductive material. However, the through-holes merely connect these signal conductors of the microwave transmission lines on the opposite surfaces of the ceramic substrate, and a microwave transmission line comprising the signal conductor and the ground conductors having a matched characteristic impedance is not achieved. That is, the through-holes 504a and 504b cause discontinuities in the microwave transmission lines from the input and output terminals 510 and 520 to the microwave IC chip 1, respectively, and mismatching of characteristic impedances occurs between the through-hole and the transmission line before or behind the through-hole, with the result that reflection of the microwave signal unfavorably increases.
Meanwhile, Japanese Published Patent Application No. 2-156702 discloses another microwave IC package provided with input and output side strip lines comprising ground conductor layers disposed on the surface of a dielectric substrate and strip conductors disposed on the rear surface of the substrate, in place of the input and output side coplanar transmission parts 550 and 560 and the input and output side microstrip transmission parts 570 and 580 of the microwave IC package described with respect to FIGS. 10.about.12. Also in this IC package, the strip conductors on the rear surface of the dielectric substrate are connected to the microwave IC chip by through-holes penetrating the dielectric substrate, so that the through-holes cause discontinuities in the transmission lines, whereby mismatching of characteristic impedances occurs between the through-hole and the transmission line before or after the through-hole.
Furthermore, Japanese Published Patent Application No. 4-38855 discloses another microwave IC package in which a microwave IC chip is disposed on a package body and dielectric films whereon coplanar lines are formed are provided as input and output terminals of the package. In this structure, a continuous transmission mode is obtained through the microwave transmission line from the transmission line on the package substrate to the microwave IC chip, but the connection between the coplanar line on the dielectric film and the coplanar line on the package substrate is not easily made by solder or the like because the dielectric film should be pressed onto the package substrate by pressure means.